just thinking how to minimize the size of my site.i use google pagespeed insight and it said i must compress the several images of my site.i try several ways to compress the images with software compression.but it make the images more bad and have a lower quality.after search the solution on google,i found some new image format.it called .webp.it can decrease the size of the images.like this one :

and the important is,.webp format is from google it self.google make .webp to replace another format for better perfomance on load site.but remember,on .webp image,make a link to .jpeg.so user can view it on they PC.